A 3rd Generation Partnership Project (3GPP) Evolved Packet System (EPS) consists of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW or PDN GW), a Home Subscriber Server (HSS), a 3GPP Authentication, Authorization and Accounting (AAA) server, a Policy and Charging Rules Function (PCRF) entity and other support nodes.
FIG. 1 shows a first diagram of the connection of a wireless communication network according to relevant technology, wherein the MME takes charge of the related work of control plane, such as mobility management, processing of non-access layer signaling and context management in user mobility management; the S-GW is an access gateway device, which is connected with the E-UTRAN and is configured to forward data between the E-UTRAN and the P-GW and take charge of the caching of paging waiting data; the P-GW is a border gateway of the EPS and Packet Data Network (PDN) and takes charge of the access of the PDN and the data forwarding between the EPS and the PDN; both S-GW and P-GW are core network gateways.
Home (e)NodeB is a small low-power base station, which is deployed in indoor places such as home and office, with a main purpose of providing a higher service speed for a user, reducing the expense associated with a high-speed service, and meanwhile remedying the coverage shortage of an existing distributed cellular wireless communication system. The Home (e)NodeB has advantages of affordable price, convenience, low-power output, and plug and play, etc.
FIG. 2 shows a second diagram of the connection of a wireless communication network according to relevant technology; in a Home (e)NodeB system, the Home (e)NodeB is a wireless side network element, wherein the Home (e)NodeB can be directly connected to the core network, as shown in FIG. 1; the Home (e)NodeB also can be connected to the core network through a logic network element such as a Home (e)NodeB gateway, as shown in FIG. 2; the Home (e)NodeB gateway mainly has the functions of: verifying the security of the Home (e)NodeB, processing the registration of the Home (e)NodeB, maintaining and managing the Home (e)NodeB, configuring and controlling the Home (e)NodeB according to the requirement of an operator, taking charge of data exchange between the core network and the Home (e)NodeB.
In the Home (e)NodeB system, there is a concept of Closed Subscriber Group (CSG) which allows the user to access one or more access restricted CSG-cells. The operating mode of the Home (e)NodeB can be divided into a closed mode, a hybrid mode and an open mode. When the Home (e)NodeB is in closed mode, only the CSG users belonging to the Home (e)NodeB can access the base station and enjoy the services provided by the base station; when the Home (e)NodeB is in open mode, any user can access the base station, at this moment, the Home (e)NodeB is equivalent to a macro base station in usage; when the Home (e)NodeB is in hybrid mode, both CSG users and other user are allowed to have an access, but the user types are differentiated according to whether the user belongs to the CSG list so as to realize differentiated Quality of Service (QoS) process, that is to say, the CSG users have a higher service priority and have better QoS and service types when using the hybrid mode of Home (e)NodeB.
Besides supporting the access of the mobile core network, the mobile communication system (including the Home (e)NodeB) also can support an IP offload function (for example, the IP offload can be a local IP access), under the conditions that the wireless side network element has an IP offload capability and the user subscription allows IP offload, the local access of a UE to other IP devices of the home network or the internet can be realized.
The implementation of IP offload can provide a strong support for the data offload technology by adding a local gateway; as a gateway of the local access to external network (for example, internet), the local gateway provides functions such as address allocation, charging, packet filtering, policy control, traffic offload function, NAS/S1-AP/Radios Access Network Application Part (RANAP)/General Tunneling Protocol (GTP)/Proxy Mobile IP (PMIP)/Mobile IP (MIP), message resolution, Network Address Translation (NAT), and IP offload policy routing and execution, etc. The local gateway can be integrated with/separated from the wireless side network element (as shown in FIG. 1).
FIG. 3 shows a third diagram of the connection of a wireless communication network according to relevant technology; as shown in FIG. 3, under the condition that a Home (e)NodeB gateway exists, the local gateway not only can be integrated with/separated from the Home (e)NodeB, also can be separated from/integrated with the Home (e)NodeB gateway. The local gateway can be a Local SGW (L-SGW) and a Local PGW (L-PGW), can be a single L-SGW, and can be a traffic offload function entity. In addition, the Home (e)NodeB gateway can be integrated with the Home (e)NodeB. For a Universal Terrestrial Radio Access Network (UTRAN) system, the core network gateway can be a Serving GPRS Support Node (SGSN), a Gateway GPRS Support Node (GGSN). The local gateway can be a Local GGSN (L-GGSN) and a Local SGSN (L-SGSN), can be a single L-GGSN and can be a traffic offload function entity.
FIG. 4 shows a diagram of the local IP access data stream of a wireless communication system according to relevant technology; as shown in FIG. 4, taking a Long Term Evolution (LTE) mobile communication network architecture for example, the schematic data streams of the IP offload and the core network connection in the wireless communication system shown in FIG. 1 are illustrated.
FIG. 5 shows a flowchart of the interaction of a UE performing a handover process according to relevant technology; as shown in FIG. 5, based on the scene of the system architecture shown in FIG. 1, the interaction comprises the following Steps 502 to 508:
Step 502: a wireless side network element determines to initiate an S1 handover.
Step 504: an source wireless side network element sends a handover required message to an source MME.
Step 506: the source MME sends a forward relocation request message to a target MME.
Step 508: the target MME initiates a session establishment flow of the core network and the IP offload connection.
Step 510: the target MME requests a target wireless side network element to perform the handover (that is, by sending a handover request).
Step 512: the target wireless side network element responds a handover request acknowledge message to the target MME.
Step 514: the target MME sends a forward relocation response message to the source MME.
Step 516: the source MME sends a handover command to the source wireless side network element.
Step 518: the source wireless side network element sends a handover command to a UE.
Step 520: the UE initiates a handover confirm message to the target wireless side network element.
Step 522: the target wireless side network element notifies the target MME to perform the handover (that is, by sending a handover notify).
Step 524: the target MME sends a forward relocation complete notification message to the source MME.
Step 526: the source wireless side network element returns a forward relocation complete acknowledge message to the target MME.
Step 528: continue the normal handover flow.
Under the condition that the UE simultaneously has a core network connection and an IP offload connection, the MME needs to provide support for the normal establishment and maintenance of the IP offload connection; however, if the UE switches from an MME supporting IP offload to an MME not supporting IP offload, a phenomenon of handover failure of the core network connection might be caused, thus the core network service data is interrupted and the experience of the user is greatly reduced.